[RFC] OpenSSL AEAD support View as Markdown

+1 thanks Jakub!

Hi,

Hi Jakub,

https://wiki.php.net/rfc/openssl_aead

I think the API might need to be more generic so that any future cipher
modes with different parameters could also be passed in.

The reference model I'd suggest is the "context" parameter passed to
stream related-functions. Userland creates a context, then passes the
context to the encrypt/decrypt functions. The context is specific to the
wrapper and drives specific behavior. Encrypt can add to the context any
specific cipher state that needs to be passed along to decrypt.

Using this model, the openssl API might look like:

$context = openssl_context_create([ 'aead' => [ 'aad' => '...',
'tag_length' => '...' ]]);
$ciphertext = openssl_encrypt(
$data, $method, $password, $options, $iv,
$context // here is the new parameter, encapsulating all cipher
specifics
);

echo $context['aead']['tag']; // populated by openssl_encrypt

$plaintext = openssl_decrypt(
$ciphertext, $method, $password, $options, $iv,
$context // fully-reversible, because all necessary data are in
context
);

Please see note in https://wiki.php.net/rfc/openssl_aead#rejected_features
. Any context related features will add a lot to the size of the
implementation. In this case it would also mean introducing an object with
dimension handler to the openssl ext which doesn't really match with the
rest of the extension API. The proposed API is more conformant to the rest
and the code addition is also limited which is very important from the
maintenance point of view.

I have got already an extension where you can do all of this context
related stuff ( see https://github.com/bukka/php-crypto ) but I don't
think
that anything like this should be part of the openssl ext. I think we
should concentrate on adding just the most important features with minimal
code addition to openssl ext and also concentrate on the fixing the actual
bugs. Bare in mind that all of this has to be maintained for very long time
and when you look to the regular contributors to openssl ext, you won't see
too many people...

To sum it up this is a minimal proposal to add AEAD support to openssl ext.
Anything context related is out of scope of this RFC.

Cheers

Jakub

Hi,

I think the API might need to be more generic so that any future cipher
modes with different parameters could also be passed in.

Please see note in
https://wiki.php.net/rfc/openssl_aead#rejected_features . Any context
related features will add a lot to the size of the implementation. In this
case it would also mean introducing an object with dimension handler to the
openssl ext which doesn't really match with the rest of the extension API.
The proposed API is more conformant to the rest and the code addition is
also limited which is very important from the maintenance point of view.

Ok, a context resource may not be pragmatic. Perhaps a compromise in the
form of a thin wrapper:

string openssl_encrypt_aead(string $data , string $method , string
$password [, int $options = 0 [, string $iv = "" [, string &$tag = "" [,
string $aad = "" [, int $tag_length = 16 ]]]])

string openssl_decrypt_aead(string $data , string $method , string
$password [, int $options = 0 [, string $iv = "" [, string $tag = "" [,
string $aad = "" ]]]] )

This actually feels more right anyway: openssl_encrypt only does
encryption, whereas openssl_encrypt_aead does encryption and integrity.
I would hate for users to pass a method of aes128 and think they can forgo
an HMAC because they thought PHP would give them back a valid tag.